1. Field of the Invention
The present invention relates to a relatively non-invasive plaque resolving device of the class adapted to be inserted through the lumen of a blood vessel and manipulated therethrough to a desired location to ply a cutting tool to excise deposits of atherosclerotic plaque from the internal surfaces of the vessel. More particularly, the present invention relates to an improved cutting tool for use in such a system.
2. Related Art
Impairment of the circulation of blood occasioned by intraarterial deposits of atherosclerotic plaque is a major symptom of cardiovascular disease. Obstruction of coronary arteries can lead to tissue death because of oxygen deprivation of heart muscle. Coronary infarction (heart attack) is the result. Plaque-induced stenosis of other major arteries can result in impairment of peripheral organ function. One long-used procedure for overcoming such obstructions and blockages involves a surgical by-pass operation in which the obstructed arteries are subtended by patient autographed blood vessels removed from other parts of the patient's body. Surgically invasive endarterectomy has also been used with limited success for clearing obstructed vessels.
The need has long existed for a less invasive and radical procedure to alleviate such blockages and achieve transmyocardial revascularization, or the like, in a manner which causes no significant damage to the healthy endothelial lining of the surrounding vessel. One technique that attempts to fulfill this need is balloon angioplasty in which an inflatable balloon is passed to the stenotic region of the affected artery and inflated with a fluid to a pressure (normally, about 5 atmospheres) to depress the plaque against the arterial wall thereby opening up the arterial volume. Because circulation is grossly impaired, however, balloon inflation/deflation must occur in a matter of seconds to avoid infarction. In addition, limited force is available because of the fear of damage to the arteries caused by overpressurization of the balloon. Also, the capture of plaque debris that may slough during the expansion process is not as yet provided for by such devices.
Other approaches include the use of a laser to clear obstructions in vessels as proposed, for example, in U.S. Pat. No. 4,207,874 to Choy. In that device, laser energy is conveyed by flexible fiberoptics in conjunction with a vascular catheter and applied to the plaque obstruction in the occluded zone. In conjunction with this system various axial channels may be provided with appropriate fluid management manifolds in order to inject saline, aspirate debris with the saline and inject dye for visualization. Additional coherently aligned fibers may be provided for actual viewing of the obstruction intraluminally. In addition to Choy, many other approaches utilizing variations on a laser excising system have also been proposed. Lasers, for example, have been utilized to resolve plaque by heating a catheter tip in a manner which causes the plaque tissue to, in effect, be melted away by the heated tip of the catheter resulting in permanent removal. That approach is illustrated by Hershenson in U.S. Pat. No. 4,748,979.
A variety of cutting devices have also been proposed in conjunction with catheters in which rotating cutters actually address and excise the stenosis. Presently known devices, however, have not been able to combine the required ability to achieve rapid cutting of the stenosis with the equally important ability to do so without a high degree of risk of affecting or damaging the relatively soft adjacent wall of the arterial vessel involved.
One such device is disclosed in U.S. Pat. No. 4,784,636 to Rydell which is assigned to the same assignee as the present invention. That invention provides an atherectomy catheter which includes a guide catheter having an inflatable balloon disposed on the distal end portion thereof, the guide catheter being dimensioned to receive an elongated drive tube having an angular cutting tip affixed to the distal end thereof. A rotational drive mechanism is coupled to the drive tube at its proximal end for rotating the cutting tip. Provision is also made in the drive mechanism for introducing fluid through the lumen of the guide catheter for inflating the balloon and for drawing a vacuum on the lumen of the drive tube for aspirating the treatment site. In use, the guide catheter with the drive tube and cutter head retracted is advanced up to the occlusion and then, the balloon is inflated to lock the distal end in place. Next the cutter is rotated at high speed and advanced into the occlusion, while blood and any loose particular matter is aspirated. The balloon is then deflated and advanced further into the lesion and the steps repeated until the occlusion is removed.
A more recently issued patent to Rydell, also of common assignee with the prior above-referenced patent, is U.S. Pat. No. 4,857,045 which is directed to a self-guiding atherectomy catheter system utilizing coaxial inner and outer flexible tubular members in which the inner tubular member is journaled for rotation at the distal end of the outer tubular member. A motor located at the proximal end of the catheter assembly drives the inner tubular member including a cutter head fixed to the inner tubular member at a point just beyond the end portion of the outer tubular member. Aspiration is accomplished through the inner tubular member and a flushing fluid such as saline administered through the outer tubular member, as required.
That reference further discloses a dome-shaped rotational cutting head containing a large number of substantially round open ports for addressing blockage material upon rotation. When the cutting head is rotated, the open ports directly address the plaque but are not precluded from cutting into the arterial lining and wall if extreme care is not taken with respect to the use of the device.
While the last-discussed system represents an improvement with regard to centering and operating the atherectomy catheter within a vessel of interest, there remains a need to improve the safety of cutting devices of the class described with respect to reducing and preventing damage to the vessel of interest including its inner lining which may be occasioned when removing a stenosis. There also exists a need to improve the ability of the operator to guide the catheter in navigating the vascular system to reach the situs of the occlusion of interest. Guidewires have been used with success in several types of catheters but heretofore have not been used with rotating atherectomy devices because of the need to coordinate the guidewire placement to avoid the cutter head.